The present invention is directed to a torque transmission driver used to transmit torque from a torque generating source, such as a power driver, to a fastener for assembly of a structure or device.
Torque transmission drivers for torque transmitting systems and fasteners used in those systems are well-known in the art. The bit of the driver had a recess or a projection of a particular shape which fit a complimentary shaped projection or recess in the fastener. One of the more commonly known torque transmitting systems was the cruciform type drive system commercialized as the PHILLIPS® drive system. See for example, U.S. Pat. No. 2,046,837. Numerous forms and shapes of torque transmitting drive systems have been proposed. See for example, U.S. Pat. No. 2,397,216. In addition, some prior drive systems included three blades or lobes. See for example, U.S. Pat. Nos. 4,084,478, and 8,182,187.
Spline-type torque transmitting systems of four-lobe, five-lobe and six-lobe have been well-known. Examples of these four-lobe, five-lobe and six-lobe torque transmitting systems, with their fasteners and drivers, are described in U.S. Pat. Nos. 2,969,250; 3,187,790; 3,584,667; 4,970,922 and 5,279,190. Early versions of such spline-type torque transmission drive systems had square corners, for which corresponding fastener recesses were difficult and expensive to make and resulted in stresses in the fastener and/or driver which lead to fatigue failure with repeated use. Later versions of five and six lobe spline type torque drive systems had a plurality of intersecting oppositely curved surfaces evenly positioned about the 360° circumference of the fastener head or driver bit to form an alternating series of lobes and flutes. These latter torque drive systems overcame some of the problems inherent in the earliest spline type systems, but were not generally capable of retaining a lobe drive angle less than five degrees. Upon application of higher torques, force components would rise causing failure or strip out of the lobes from the fasteners or the drivers. One version of these later spline type torque drive systems, known commercially as the TORX® drive system, had six-lobe and five-lobe configurations based on mating arcuate surfaces designed to attain drive angles within the range of 10° to 20°. See U.S. Pat. No. 3,584,667.
A later version of this spline type torque transmission drive system reduced the drive angle to zero by having both the driven surfaces of the fastener head and the drive surfaces of the torque driver formed by a first series of elliptically curved surfaces with a second series of elliptically curved surfaces alternating there between. One series of these elliptically curved surfaces was convex, while the alternating series of elliptically curved surfaces was concave. The alternating concave and convex elliptically curved surfaces merged smoothly and tangentially to define a series of alternating flutes and lobes extending about the 360° circumference of the fastener head or the driver bit. Both the lobes and the flutes of the fastener head and driver bit were elliptically curved in section. Also, the centers of the elliptically curved lobes and corresponding centers of the elliptically curved flutes were disposed at the apexes of a regular hexagon, although not the same hexagon, due to the alternating nature of these components. See U.S. Pat. No. 5,279,190. An embodiment of this lobular torque transmission drive system has been commercially marketed as the TORX PLUS® drive system.
Certain prior torque transmission drivers have been limited by their dedication to one or a limited number of sizes of fastener having drive surfaces, with recess or projections, corresponding to the size of the driver. For example, the lobular fastener marketed under the brand name TORX® required a separate driver of a diameter to match each size of corresponding fastener. This meant that a set of the drivers had to be maintained on site by assemblers, and each time a different size fastener was installed a different size bit was retrieved from the set and installed in a torsion gun. For example, a T-1 TORX® driver was required to drive a T-1 TORX® fastener, and a T-2 TORX® driver was required to drive a T-2 TORX® fastener, and so on. Other fastener systems, such as a cruciform type system sold under the brand name PHILLIPS®, could drive more than one size fastener, but these systems were susceptible to driver cam-out from the fastener. Cam-out is a rotational lifting movement by which the driver lifts out of the fastener recess, caused when the fastener and the driver have angled surfaces that enable sliding movement between the surfaces. Cam-out by the prior torque transmission systems caused damage to the fasteners and drivers, prevented fasteners from being tightened to a proper torque, as well as generated shavings and burrs that damaged components in the assembly.
The prior systems created inefficiency for assemblers who install fasteners of different sizes who have to pick up one driver to install one size fastener and pick up another driver to install another size fastener, or alternatively attempt to drive a fastener with the wrong size driver or a driver that cams out, which added to the difficulty where not impossible. Driving a fastener with a driver that was too large or too small for the fastener prevented the driver from seating properly increasing the prospect of cam-out of the driver from the fastener, strip-out or shearing of the fastener recess or projections, and/or improperly torqued fastener installation. This presented inefficiency and waste in installation and an increased incidence of mis-installed fasteners in assemblies and failure of the assemblies. Tapered drive systems in the past of the cruciform type, e.g. PHILLIPS® drivers, were well know to cam out of fasteners under torque, causing damage to and waste of fasteners or drivers, with decreased efficiency and increased incidence of mis-installed fasteners and misassembly of products, devices and machines. Additionally, the prior spline-type systems were less effective with thread forming and thread cutting fasteners because the drivers tended to cam out of the fastener and the drivers wobbled in the fasteners not maintaining axial alignment. All of these problems were accentuated in extremely small size fastener heads and torsion drivers, particularly for fasteners with a major thread diameter smaller than about 0.063 inch (1.6 millimeter), and more particularly for fasteners with a major thread diameter smaller than about 0.039 inch (1.0 millimeter). In addition to the problems discussed above, such small fasteners tended to deform when in use because of the small size of the fasteners, the sizes of the lobes, and the clearance tolerances involved.
There remains a need for fastening systems including drivers and fasteners that address the foregoing problems.
A fastener system includes a fastener having a head with a recess, and a threaded shank, the recess defined by a series of three alternating lobes and troughs about a rotational axis, each of the alternating lobes and troughs defined by in series an outer radius portion, a drive side transition, an inner transition radius, and a reverse drive portion, the recess having a side wall defined by the outer radius portion with a taper angle of about 60° from the rotational axis; and a driver comprising a shaped tapered bit defined by a series of three alternating lobes and driver troughs about the rotational axis, each of the alternating lobes and troughs defined by in series an outer radius portion, a drive side transition, an inner transition radius, and a reverse drive portion, wherein each lobe has a tapering height and width with a substantially constant ratio of lobe width to lobe height, and wherein the driver lobes have a side wall defined by the outer radius portion with a taper angle relative to the rotational axis less than or equal to the taper angle of the recess side wall.
In some embodiments, the driver side wall has a taper angle of about 60° from the rotational axis. In some embodiments, the driver side wall has a taper angle of about 42° from the rotational axis. In some embodiments, the taper angle of the driver side wall is at least 10° less than the taper angle of the recess side wall.
In some embodiments, the drive side transition is linear and defines a drive angle relative to a radial line extending from the rotational axis and tangent to the inner transition radius. In some embodiments, the drive angle is between about 0° and 5°. In some embodiments, the drive side transition has a length between about 20% and 60% of the lobe height.
In some embodiments, the inner transition radius comprises a first segment defined by a first radius and a second segment defined by a second radius greater than the first radius.
In some embodiments, the driver comprises a tip portion and the outer transition radius is tapered at about 140° in the tip portion.
In some embodiments, the fastener system further includes a plurality of additional fasteners of different sizes, each of the plurality of fasteners having at least one cross section of a recess that is substantially the same as a cross section of the recess of the fastener, wherein the driver is configured to transmit torque to each of the fasteners.
In some embodiments, the fastener has a major thread diameter smaller than 0.039 inch (1.0 millimeter). In some embodiments, the fastener has a major thread diameter smaller than 0.063 inch (1.6 millimeter).
In some embodiments, the drive side transition of the driver is adapted to engage the drive side transition of the fastener at a lift angle less than 2° to reduce cam out.